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Output RF Spectrum Measurement Description
Last updated: May 8, 2002
The Output RF Spectrum Measurement is applicable to both GSM and GPRS. This measurement description contains two sections:
GSM Output RF Spectrum Measurement
How is an output RF spectrum (ORFS) measurement made?
ORFS is a narrow-band measurement that provides information about the distribution of the mobile station transmitter's out-of-channel spectral energy due to modulation and switching as defined in ETSI GSM 05.05, section 4.2, 3GPP 51.010 (formerly ETSI GSM 11.10), section 13.4 at offsets < 1800 kHz.
The test set's measurements include both ORFS due to modulation and ORFS due to switching. Switching and modulation measurements may be performed from the same burst. If you request both modulation and switching results at the same frequency offsets, measurement throughput is improved. Measurements are made using a 30 kHz IF bandwidth, 5-pole synchronously tuned filter.
ORFS due to modulation measures out of channel interference during the useful part of the burst excluding the midamble. The measurement returns relative results in (dB) using the power in a 30 kHz bandwidth at zero offset as the reference. You can set 0 to 22 offsets.
ORFS due to switching measures out of channel interference over the entire burst, plus up to 10 additional bits on either side of the 147 bit wide normal burst. The measurement returns absolute power results (dBm) for each offset indicating the maximum value over the entire burst. You can set 0 to 8 ORFS due to switching offsets.
The number of measurements to be averaged for each offset may be different. The test set internally controls all other aspects of the measurement, including calibration.
TX power (average power), 30 kHz bandwidth power at zero offset, ORFS due to modulation average power, and ORFS due to switching maximum power are included in an ORFS measurement, when both modulation and switching measurements are made. (TX power is performed using the same method as described in the
Transmit Power Measurement Description
, which synchronizes the measurement with the burst amplitude).
ORFS due to modulation
When multiple offsets for the ORFS due to modulation measurement are set, the DSP averages the power across the appropriate time segments (40 bits) of the burst with a 30 kHz resolution bandwidth, 5-pole, synchronously tuned filter placed at the center frequency of the burst and compares it to a time segment of the response of the same filter placed at some frequency offset. The result is a relative power measurement using the 30 kHz bandwidth power at zero offset as a reference. For each offset you specify, the DSP retunes the filter and measures the 30 kHz bandwidth power and compares it to the reference, giving a relative power measurement of signal power over the entire burst. The DSP processes the data and makes the results available to you. The 30 kHz bandwidth power at zero offset is measured only if you request at least one ORFS due to modulation measurement.
For offsets up to 1.799999 MHz, an ORFS due to modulation measurement uses the 30 kHz resolution bandwidth filter required in GSM 05.05. At the 1800 kHz offset frequency the ORFS due to modulation measurement is made using the 30 kHz resolution bandwidth filter, not the 100 kHz resolution bandwidth filter required by ETSI.
The ORFS due to modulation measurement measures both the front and back data portions of the burst. Measurements occur from bit 15 to 60 and from bit 87 to 132. GSM 11.10 recommends that this measurement is performed on only the back section of the burst. Measuring both the front and back of the burst has the speed advantage of providing two modulation measurements per burst.
ORFS due to switching
When multiple offsets for the ORFS due to switching measurement are set, the DSP tunes the 30 kHz resolution bandwidth, 5-pole, synchronously tuned filter to the first requested offset and samples the power of the signal over the entire burst. The result for this measurement is the maximum of these sampled values and is reported as an absolute power measurement. The DSP then retunes the filter, samples the signal, processes the data for each requested offset, then provides the results.
The 30 kHz bandwidth power at zero offset measurement is not made during ORFS due to switching measurements. In order to make that measurement, you must request at least one ORFS due to
modulation
measurement.
Single or Multi-Measurements
To obtain statistical measurement results, the multi-measurement count must be set for both switching and modulation measurements. (See
Statistical Measurement Results
for more information.)
Changing the multi-measurement modulation or switching count number or setting multi-measurement to ON allows the test set to make multiple measurements at each frequency offset. For modulation measurements the offset values returned are the average power at each offset. For switching measurements the offset values returned are the maximum power at each offset. If you set Multi-measurement count state to OFF only one ORFS measurement is completed at each offset (that is, one ORFS due to modulation, and one ORFS due to switching measurement).
-
If you want to make multiple ORFS due to
modulation
measurements and no ORFS due to switching measurements, a number must be entered in the multi-measurement modulation count, and all the
switching
offset frequencies must be off.
-
In order to make multiple ORFS due to
switching
measurements and no ORFS due to modulation measurements, a number must be entered in the multi-measurement switching count, and all
modulation
offset frequencies must be off.
Types of Signals ORFS can Measure
ORFS measurements can be made on these types of input signals:
-
Normal GSM TCH burst with mobile station in active cell mode.
-
Normal GSM TCH burst with mobile station in test mode.
-
Non-bursted signal including GMSK modulation with mobile station in test mode.
For a non-bursted signal, an ORFS due to switching measurement result is not useful.
Input Signal Requirements
The ORFS measurement will complete and meet its accuracy specification under the following conditions:
-
Input signal level is between -10 dBm and +43 dBm.
-
Input signal level within +/-3 dB of the expected input level.
-
Frequency is within +/-200 Hz of expected input frequency.
Trigger Source
Auto triggering is the recommended trigger source for each measurement, allowing the test set to choose the preferred trigger source. However, you may want to select the trigger source.
Recommended Trigger Source Settings
|
Input Signal Type
|
Recommended Trigger Source |
|
Normal GSM TCH burst with mobile station in active cell mode
|
Protocol |
|
Normal GSM TCH burst with mobile station in test mode
|
RF Rise |
|
CW signal |
Immediate |
GPRS Output RF Spectrum Measurement
How is an output RF spectrum (ORFS) measurement made?
ORFS is a narrow-band measurement that provides information about the distribution of the mobile station transmitter's out-of-channel spectral energy due to modulation and switching as defined in ETSI GSM 05.05, section 4.2, 3GPP 51.010 (formerly ETSI GSM 11.10), section 13.4. For GPRS mobiles which support a single uplink timeslot or two adjacent uplink timeslots, the measurement conforms to 3GPP 51.010 (formerly ETSI GSM 11.10), section 13.16.3 at offsets < 1800 kHz (when the Multi-Measurement Count - Modulation parameter is set to Off using
SETup:ORFSpectrum:COUNt:STATe[:SELected]
).
The test set's measurements include both ORFS due to modulation and ORFS due to switching.
ORFS due to modulation measures out of channel interference during the useful part of the burst excluding the midamble. The measurement returns relative results in (dB) using the power in a 30 kHz bandwidth at zero offset as the reference. You can set 0 to 22 offsets.
ORFS due to switching measures out of channel interference over the one, or two adjacent bursts in the multislot configuration, plus up to 10 additional bits on either side of the 147 bit wide normal burst. The measurement returns absolute power results (dBm) for each offset indicating the maximum value over the entire multislot configuration. You can set 0 to 8 ORFS due to switching offsets.
When measuring a single uplink timeslot, switching and modulation measurements can be performed from the same burst (provided that the overshoot in the burst is less than 1 dB). If you request both modulation and switching results at the same frequency offsets, measurement throughput is improved. Measurements are made using a 30 kHz IF bandwidth, 5-pole synchronously tuned filter.
When measuring two adjacent uplink timeslots, the modulation measurement is performed for only one burst at a time in the multislot configuration, which you specify using
RFANalyzer:MSLot:MEASurement:BURSt
. The switching measurement is performed over both adjacent bursts in the multislot configuration irrespective of which of the two bursts you have currently selected to measure.
In order for the test set to return a valid switching measurement result when measuring two adjacent uplink bursts, you should ensure that the burst you have selected to measure has a power level equal to or higher than the expected power level of the other uplink burst in the multislot configuration. If the selected burst has a lower expected power level, the same hardware range settings cannot be used for both the modulation and switching measurements and the test set returns NAN for the switching measurement. The expected power can be set manually using
RFANalyzer:MANual:POWer:GPRS[:SELected]:BURSt[1|2]
.
The number of measurements to be averaged for each offset may be different. The test set internally controls all other aspects of the measurement, including calibration.
TX power (average power), 30 kHz bandwidth power at zero offset, ORFS due to modulation average power, and ORFS due to switching maximum power are included in an ORFS measurement, when both modulation and switching measurements are made. (TX power is performed using the same method as described in the
Transmit Power Measurement Description
, which synchronizes the measurement with the burst amplitude).
ORFS due to modulation
When multiple offsets for the ORFS due to modulation measurement are set, the DSP averages the power across the appropriate time segments (40 bits) of the burst with a 30 kHz resolution bandwidth, 5-pole, synchronously tuned filter placed at the center frequency of the burst and compares it to a time segment of the response of the same filter placed at some frequency offset. The result is a relative power measurement using the 30 kHz bandwidth power at zero offset as a reference. For each offset you specify, the DSP retunes the filter and measures the 30 kHz bandwidth power and compares it to the reference, giving a relative power measurement of signal power over the entire burst. The DSP processes the data and makes the results available to you. The 30 kHz bandwidth power at zero offset is measured only if you request at least one ORFS due to modulation measurement.
For offsets up to 1.799999 MHz, an ORFS due to modulation measurement uses the 30 kHz resolution bandwidth filter required in GSM 05.05. At the 1800 kHz offset frequency the ORFS due to modulation measurement is made using the 30 kHz resolution bandwidth filter, not the 100 kHz resolution bandwidth filter required by ETSI.
The ORFS due to modulation measurement measures both the front and back data portions of the burst. Measurements occur from bit 15 to 60 and from bit 87 to 132. GSM 11.10 recommends that this measurement is performed on only the back section of the burst. Measuring both the front and back of the burst has the speed advantage of providing two modulation measurements per burst.
ORFS due to switching
When multiple offsets for the ORFS due to switching measurement are set, the DSP tunes the 30 kHz resolution bandwidth, 5-pole, synchronously tuned filter to the first requested offset and samples the power of the signal over the entire burst. The result for this measurement is the maximum of these sampled values and is reported as an absolute power measurement. The DSP then retunes the filter, samples the signal, processes the data for each requested offset, then provides the results.
The 30 kHz bandwidth power at zero offset measurement is not made during ORFS due to switching measurements. In order to make that measurement, you must request at least one ORFS due to
modulation
measurement.
Single or Multi-Measurements
To obtain statistical measurement results, the multi-measurement count must be set for both switching and modulation measurements. (See
Statistical Measurement Results
for more information.)
Changing the multi-measurement modulation or switching count number or setting multi-measurement to ON allows the test set to make multiple measurements at each frequency offset. For modulation measurements the offset values returned are the average power at each offset. For switching measurements the offset values returned are the maximum power at each offset. If you set Multi-measurement count state to OFF only one ORFS measurement is completed at each offset (that is, one ORFS due to modulation, and one ORFS due to switching measurement).
-
If you want to make multiple ORFS due to
modulation
measurements and no ORFS due to switching measurements, a number must be entered in the multi-measurement modulation count, and all the
switching
offset frequencies must be off.
-
In order to make multiple ORFS due to
switching
measurements and no ORFS due to modulation measurements, a number must be entered in the multi-measurement switching count, and all
modulation
offset frequencies must be off.
Measuring ORFS on GPRS mobiles using the BLER data connection type
The result of the Output RF Spectrum measurement relies on pseudo random data being present in the data field of the RF burst. When using the BLER data connection type, these data fields do not contain pseudo random data, therefore the results may not be representative.
Types of Signals ORFS can Measure
The following list summarizes the input signal attributes and mobile station operating modes for making PvT measurements.
-
All supported GPRS PDTCH multislot configurations with the mobile station in active cell mode.
-
All supported GPRS PDTCH multislot configurations with the mobile station in GPRS BCH or GPRS BCH+PDTCH test mode (no protocol).
-
Non-bursted signal including GMSK modulation with mobile station in test mode.
For a non-bursted signal, an ORFS due to switching measurement result is not useful.
Input Signal Requirements
The ORFS measurement will complete and meet its accuracy specification under the following conditions:
-
Input signal level is between -10 dBm and +37 dBm.
-
Input signal level within +/-3 dB of the expected input level.
-
Frequency is within +/-200 Hz of expected input frequency.
Trigger Source
Auto triggering is the recommended trigger source for each measurement, allowing the test set to choose the preferred trigger source. However, you may want to select the trigger source.
Recommended Trigger Source Settings
|
Input Signal Type
|
Recommended Trigger Source |
|
GPRS PDTCH multislot configuration with mobile station in active cell mode
|
Protocol |
|
Normal GPRS PDTCH multislot configuration with mobile station in GPRS BCH or GPRS BCH+PDTCH test mode
|
RF Rise |
|
CW signal |
Immediate |
For more information on measurement triggering, refer to
Triggering of Measurements
.
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